Sabin Corneliu Buraga [email protected]

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1 | Sabin Corneliu Buraga - [email protected]

Research Studies on Semantic Web

Sabin Corneliu Buraga [email protected]

http://www.infoiasi.ro/~busaco/

Faculty of Computer Science

“Al.I.Cuza” University of Iasi, Romania

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Topics

• Seeds of the Semantic Web

• Extensible Markup Language (XML)

• Resource Description Framework (RDF)

• Semantic Web

• Our Research

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Seeds of the Semantic Web

• Web 1.0 (1990)

– Tim Berners-Lee (CERN) develops a minimal hypertext system for

the Internet using Vannebar Bush’s idea of universal tool for human knowledge storage - MEMEX (‘45)

– client/server architecture – hypertext ≡ hypermedia

(Ted Nelson, 1965)

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Seeds of the Semantic Web

• Origin and Goals of the Web

– Human communication thru shared knowledge

– Exploitation of computing power in real life

• Web Architecture

– Resources are identified by

URIs (Uniform Resource Identifiers) – Internet protocols (e.g. HTTP) allow

representation to be looked up – Documents parsed as markup – Markup contains URIs

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Seeds of the Semantic Web

• Revolutions

– The HTML Revolution shared information space – The XML Revolution

culture of open exchange of information – The RDF Revolution

foundation of the Semantic Web

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Seeds of the Semantic Web

• The XML Revolution

– “XML is the ASCII of the future”

(Tim Bray, XML Files, oct.’98)

– Meta-language (subset of SGML) – XML adds type and structure to

information

– Simple, flexible, and suitable

for Web applications (platform independent) – Formal description: Document Type

Definition, XML Schema, namespaces – Universal industry support

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Seeds of the Semantic Web

• The XML Revolution

– XML is a simple data format that balances the needs of people to read/write data with needs of machine to read/write data

<elementName attributeName=“value”>

<empty />

</elementName>

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Seeds of the Semantic Web

• XML family

– Syntax: XML (1998, 2000)

– Validation: DTD, namespaces (1999), XML Schema (2000)

– Hyper linking:

XLink (2000), XPointer (2000)

– Transformations and semantics:

XSL - Extensible Stylesheet Language (2001)

uses XPointer and XSLT languages

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Seeds of the Semantic Web

• Processing XML

– Document Object Model (DOM)

• XML document as an abstract tree of objects

• Implementation independent

• Very complex and feature-rich

• DOM - level 1 (1998), DOM - level 2 (2000),...

– Simple API for XML (SAX)

• XML document as a flow of element-events

• More suitable for small applications

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Seeds of the Semantic Web

• The RDF Revolution

– Standardized foundation for processing metadata Metadata=data about data

– World-Wide Web Consortium’s recommendation (Lassila and Swick, 1999)

– Consists of a model for representing named properties and property values – Based on classes

– A collection of classes = RDF schema

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Seeds of the Semantic Web

• Resource inspection

• Data investigation

• Intelligent agents

• Intellectual property rights

• Personal/general security (digital signatures)

Intelligent structures Knowledge

representation Standar-

dization Semantic

Web

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Seeds of the Semantic Web

• RDF Model: unordered set of triples

– Resources

named by URIs (Uniform Resource Identifiers) – Properties

specific aspects/attributes/relations used to express resources

– Statements

{subject, predicate, object}

subject=resource, predicate=property, object=value of property

• Semantics = assertions

• Vocabulary = resources, properties

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Seeds of the Semantic Web

• RDF model provides an abstract framework for defining and using metadata

• Concrete syntax is based on XML

• Example:

“Sabin is the owner of his Web page.”

<rdf:RDF>

<rdf:Description about="http://www.infoiasi.ro/~busaco/">

<s:Owner>Sabin Corneliu Buraga</s:Owner>

</rdf:Description>

</rdf:RDF>

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Seeds of the Semantic Web

• The RDF Revolution

– Most important goal:

to denote semantics for data based on XML in a homogeneous,

platform-independent, and object-oriented way

– To give support for Tim Berners-Lee’s

Semantic Web (2001)

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Semantic Web

• Ideas

– The essential property of the WWW is its universality: “anything can link to anything”

– For the Semantic Web to function, computers must have access to structured collections of information and sets of inference rules that they can use to conduct automated reasoning

⇒ new models for knowledge representation – “The Semantic Web will enable machines

to comprehend semantic documents and data, not human speech and writings.”

(Tim Berners-Lee, 2001)

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Semantic Web

• Solutions

– Ontologies

“An ontology is a specification of a conceptualization.” (Tom Gruber)

• Ontolingua (1993)

• SHOE - Simple HTML Ontology Extension (1997)

• OIL - Ontology Interfence Layer (2000) based on description logics

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Semantic Web

• Solutions

– Agents

• “Agent” as an Ascription

“The concept of agent embodied in humans helping humans is often one where expertise is indeed mixed with knowledge of you.”

(Nicholas Negroponte, 1997)

• “Agent” as a Description

A software entity which functions continuously and autonomously in a particular environment, often inhabited by other agents and

processes.

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Semantic Web

• Solutions

– Using properly designed Web agents,

“the Semantic Web can assist

the evolution of human knowledge as a whole.” (Tim Berners-Lee, 2001)

– The consumer and producer agents

can reach a shared understanding by

exchanging ontologies, which provide

the vocabulary needed for discussion.

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Our Research

• The essential property of the WWW is its universality:

“anything can link to anything”

• Goal:

– A formal approach to model spatial and temporal relations between (fragments) of Web sites

– The model will be processed by machines

in a platform-independent way

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Our Research

• Past and present

– Modeling (spatial) relationships between different Web resources - i.e. files stored on a particular (distributed) file system:

• RDF descriptions of a distributed file system

– Searching for different structures of Web documents

• Encoding structural information of a Web page by using XML markups

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Our Research

• Present and future

– Modeling temporal relationships between (fragments of) Web sites to study

the evolution of a distributed (multimedia) Web resources

• Temporal Logics - Interval Temporal Logic (Allen, 1984)

• Temporal Logic of Actions (Lamport, 1991)

• Temporal Petri Nets?

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Our Research

• Future

–To assign actions for each temporal change of the Web site’s

structure/state

–The RDF model based on this

approach can emphasis the dynamics

of the (local) Web

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References

• T.Berners-Lee - “Weaving the Web”, Cambridge Massachusetts, 1999

• S.C.Buraga - “Web Technologies”

(in Romanian), Matrix Rom, Bucharest, 2001

• Semantic Web: http://www.SemanticWeb.org

• W3C Technical Reports, Boston, 2001:

http://www.w3.org/TR/

• For other information, see

http://www.infoiasi.ro/~busaco/

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